1. Field of the Invention
The present invention relates to a light reflective photo-electric sensing system including a method and system for sensing objects, which can be light reflective surfaces, within the system and providing an actuation signal if objects are present. The method and system can be used in a non-contact type sensor entrapment protection system.
2. Description of Related Art
Non-contact type sensor entrapment systems are known. U.S. Patent Application Publication No. 2011-0049339-A1, hereby incorporated by reference into this application, describes a photo-electric eye safety system used in conjunction with a motorized barrier operator system having a primary photo-electric eye safety device, which includes a primary emitter mounted at one side of an opening enclosed by the barrier, and a primary receiver mounted on another side of the opening and aligned to receive a beam from said primary emitter. A controller monitors the primary emitter and the primary receiver, and initiates corrective action if the beam is interrupted. A prior art non-contact sensor system 10 includes transmitter/receiver units 12 installed into photo-electric wall mounting units 13, as shown in FIG. 1. Transmitter unit 14 emits light beam 15 that is received by receiver unit 16. Sensor 17 is activated by interrupting light beam 15.
According to the UL Standard for Safety for Door, Drapery, Gate, Louver, and Window Operators and Systems, UL 325, paragraph 30.1.1, any automatically operated commercial/industrial door operator has to be connected to an external entrapment protection device. In paragraph 30.2.1, the standard states that an external entrapment protection device provided with, or as an accessory to, a commercial/industrial operator (or system) shall consist either of a contact type sensor or a non-contact type sensor.
It has been found that light reflective surfaces, such as metallic vehicle surfaces, can reflect light to the transmitter/receiver units thereby compromising the conventional photo-electric eye safety system. It is desirable to provide a method and system for sensing light reflective surfaces in a light reflective photo-electric sensing system. The system can be used to comply with the impact test of UL 325.